(i) Field of the Invention
The present invention relates to composite fine particles comprising a metal and an electroconductive polymer and a method for preparing the same.
(ii) Description of the Prior Art
Metal fine particles are being used nowadays in many advanced technical fields and they are one important raw material for which applications are now being researched and developed. Typical applicable fields of these fine particles include magnetic materials, electrode materials, magnetic fluids, jet fuels, additives for alloys, electroconductive coating materials, catalysts, intracellular dyes, materials for cell segregation, carriers for medicines, and electroconductive fillers for rubbers, plastics and fibers. In recent years, the above-mentioned metal fine particles are also expected as non-linear optical materials.
Such metal fine particles can usually be manufactured by a gaseous phase method or a liquid phase method. The metal fine particles are directly employed as raw materials for bulk materials such as the magnetic materials and electrode materials without any further treatment, but in other applications, they are often dispersed in a medium such as an organic material prior to their utilization.
Generally, the surface of a metal has a very high activity, and therefore it is often oxidized immediately when exposed to air. Among others, the specific surface area of the metal fine particles is much larger as compared with bulks, and for this reason, it is unavoidable that the surface oxidation has a great influence on products. Thus, the metal fine particles are usually stored in an inert gas such as nitrogen. Even if the activity of the metal fine particles is not so high, these particles tend to ignite immediately when brought into contact with air, or in an extreme case, they are in danger of exploding. Therefore, sufficient care is required not only at the time of the above-mentioned storage but also at the handling of the particles. In consequence, the cost increase for the safe assurance is not negligible.
Furthermore, the metal fine particles have very strong cohesive properties in themselves, and therefore, it is one of factors for a manufacturing technique how the cohesion is prevented in the manufacturing process of the fine particles and how a small particle size of the particles is maintained stably. In addition, also in the case that the metal fine particles are dispersed in an organic material or the like, the tendency of the cohesion is strong. Therefore, in order to maintain the desired small particle diameter in the dispersion, it is necessary to subject the particles to a pretreatment with a surface active agent.
In addition, the very small particle diameter on a nanometer level is required in certain application fields in which the metal fine particles are employed. As the manufacturing method of the metal fine particles which are applicable to such fields, there has been mainly used a gaseous phase method, but usually in this gaseous phase method, a manufacturing cost is high, and therefore the application fields are limited for an economical reason.